From a fish-eye view, rice fields in California's Yolo Bypass provide
an all-you-can-eat bug buffet for juvenile salmon seeking nourishment
on their journey to the sea. That's according to a new report
detailing the scientific findings of an experiment that planted fish
in harvested rice fields earlier this year, resulting in the fattest,
fastest-growing salmon on record in the state's rivers.

The report, provided to the U.S. Bureau of Reclamation, describes
three concurrent studies from researchers at the University of
California, Davis, nonprofit California Trout and the California
Department of Water Resources. The scientists investigated whether
rice fields on the floodplain of Yolo Bypass could be managed to help
recover California's populations of Chinook salmon, and if so, the
ideal habitats and management approaches that could allow both fish
and farms to thrive.

"We're finding that land managers and regulatory agencies can use
these agricultural fields to mimic natural processes," said co-author
Carson Jeffres, field and laboratory director of the Center for
Watershed Sciences at UC Davis. "We still have some things to learn,
but this report is a big step in understanding that."

Researchers found that the fish did not have a preference among the
three rice field types tested: stubble, plowed and fallow. The food
supply was so plentiful that salmon had high growth rates across
habitats and management methods.

"It's like a dehydrated food web," said Jeffres of the harvested rice
fields. "Just add water. All of those habitats are very productive
for fish."

The salmon did demonstrate a preference for habitats with better
water flow. Jeffres compared it to choosing among three good
restaurants: Each offers good food with hearty portions, but one has
better ambience and so is chosen above the others. In this case, the
better water flow was the ambience the fish preferred.

Average growth rates during the study's 41 days were the highest
recorded in freshwater in California. Growth of juvenile Chinook
averaged 0.93mm per day, with growth of 1.5 mm per day observed
during specific two-week intervals.

Mortality was greater than in the team's previous 2012 study at
Knaggs Ranch. In the 2013 study, between 0 and 29 percent of
free-swimming fish survived, while 35-98 percent of fish in
enclosures survived.

Lower survival rates were attributed to bird predation. The winter
of 2013, when the study was conducted, was one of the driest on
record in the Sacramento Valley, which may have drawn more birds to
the inundated rice fields, and to the fish. The study plots were also
relatively shallow, providing little escape for fish. A follow-up
study planned for 2014 will explore the role of depth as a refuge for
fish against avian predators.

Fish reared in plowed rice fields grew faster than those reared
over stubble or weedy vegetation. However, all habitat types were
beneficial to the fish, suggesting farm managers may have more
flexibility in land treatment after harvest.

"These results are good news for the effort to rebuild salmon
populations in California," said lead author Jacob Katz, a biologist
with California Trout. "We've always suspected that when we mimic
natural flood processes in agricultural fields, we give these fish a
food-rich habitat they recognize and thrive in. These findings
support that theory and provide a strong path forward for California
land use planners, conservationists and farmers alike. This is a
win-win model that can be replicated around the state."

The Yolo Bypass is the Central Valley's largest contiguous floodplain
and provides critical fish and wildlife habitat, the report said. It
is covered by floodway easement held by the state of California,
making other land uses subservient to flood control. Agriculture is a
major land use in the bypass, with rice the primary crop.

More than 95 percent of Central Valley floodplain habitat that was
historically used to rear juvenile Chinook salmon has been altered,
primarily diked, and drained for agriculture conversion. Most former
floodplain wetlands are now only inundated during major floods. The
report said access to floodplain habitats and the high growth rates
associated with them during even a limited time may be critical in
improving return rates for Central Valley salmon populations.

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The project was completed in collaboration with landowner partners
Cal Marsh and Farm Ventures and Knaggs Ranch, with funding from
California Trout, Knaggs Ranch LLC, Metropolitan Water District of
Southern California, Resources Legacy Fund, State and Federal
Contractors Water Agency, and the U.S. Bureau of Reclamation.

About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research
and public service that matter to California and transform the world.
Located close to the state capital, UC Davis has more than 33,000
students, more than 2,500 faculty and more than 21,000 staff, an
annual research budget of nearly $750 million, a comprehensive health
system and 13 specialized research centers. The university offers
interdisciplinary graduate study and more than 100 undergraduate
majors in four colleges -- Agricultural and Environmental
Sciences, Biological Sciences, Engineering, and Letters and Science.
It also houses six professional schools -- Education, Law,
Management, Medicine, Veterinary Medicine and the Betty Irene Moore
School of Nursing.

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